login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Composite numbers k = concat(x,LSD(k)) such that the sum of the aliquot parts of k is equal to the sum of the aliquot parts of x.
0

%I #18 Oct 13 2017 06:13:26

%S 1711,22991,109999,112639,130733,269119,318293,390319,1138399,1319519,

%T 1841839,2010719,2311919,2581871,6493519,7355839,7533599,8332399

%N Composite numbers k = concat(x,LSD(k)) such that the sum of the aliquot parts of k is equal to the sum of the aliquot parts of x.

%e sum_aliquot_parts(22991) = 361 and sum_aliquot_parts(2299) = 361.

%p with(numtheory): P:=proc(q) local n,p,x; for n from 2 to q do

%p if not isprime(n) then x:=trunc(n/10); if sigma(n)-n=sigma(x)-x then print(n); fi; fi; od; end: P(10^6);

%Y Cf. A010879 (LSD), A001065 (sum of aliquot parts)

%K nonn,base,more

%O 1,1

%A _Paolo P. Lava_, Oct 10 2017